Fire design of steel-reinforced CFST stub columns with high-strength materials

Abstract

Innovative composite sections are gaining popularity as they reduce the environmental impact of construction and take advantage of the collaboration of concrete and steel properties at room temperature and in fire. By introducing high-performance materials, these synergies are boosted. One typology is the steel-reinforced concrete-filled steel tubular (SR-CFST) section, in which a steel profile is embedded inside a CFST section. Despite their impressive load-bearing capacity and fire resistance, the available investigations on their thermo-mechanical capabilities are scarce. The present paper develops a numerical model to analyse the thermo-mechanical behaviour of SR-CFST stub columns subjected to fire. The model is validated against previous experiments conducted by the authors by comparing the temperature distribution and the mechanical behaviour with the experimental measurements. Afterwards, an extensive parametric study (1440 cases) is conducted to analyse the influence of several geometrical parameters – cross-sectional shape, outer tube dimensions and thickness, inner steel profile dimensions, section factor – and the use of high-strength materials for the concrete and the inner steel profile. Afterwards, a simplified temperature distribution proposal formerly designed by the authors for SR-CFST sections was tentatively tested. Based on this previous simplified temperature field and in line with the current provisions of EN1994-1-2, a new proposal is developed to evaluate the cross-sectional plastic resistance of SR-CFST stub columns under a fire scenario. This method unifies the initially developed thermal method and provides practical guidance for designers to evaluate the thermo-mechanical behaviour of SR-CFST columns, filling an existing gap in the European design code.